The present application relates to the field of spinal implants and, in particular, anterior vertebral implant locking devices and methods and systems for immobilizing a spinal motion segment by engaging an anterior vertebral implant locking device to same.
The spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column comprises a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior, the laminar arch, which covers the neural structures of the spinal cord and nerves for protection. Each vertebral body has relatively strong bone comprising the outside surface of the body (cortical) and relatively weak bone comprising the center of the body (cancellous). Between each vertebral body is an intervertebral disc, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine.
Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disc or the articulating joints, traumatic disruption of the disc, bone or ligaments supporting the spine, tumor or infection. In addition, congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurologic damage if the conditions are not treated appropriately.
In the treatment of diseases, injuries or malformations affecting spinal motion segments, and especially those affecting disc tissue, it has long been known to remove some or all of a degenerated, ruptured or otherwise failing disc. In cases involving intervertebral disc tissue that has been removed or is otherwise absent from a spinal motion segment, corrective measures are indicated to insure the proper spacing of the vertebrae formerly separated by the removed disc tissue.
In some instances, the two adjacent vertebrae are fused together using transplanted bone tissue, an artificial fusion component, or other compositions or devices. One potential side effect of spinal fusion procedures that has raised concerns in the medical community is that the bio-mechanical rigidity of intervertebral fusion may predispose neighboring spinal motion segments to rapid deterioration. More specifically, unlike a natural intervertebral disc, spinal fusion prevents the fused vertebrae from pivoting and rotating with respect to one another. Such lack of mobility tends to increase stresses on adjacent spinal motion segments. Additionally, several conditions may develop within adjacent spinal motion segments, including disc degeneration, disc herniation, instability, spinal stenosis, spondylosis and facet joint arthritis. Consequently, many patients may require additional disc removal and/or another type of surgical procedure as a result of spinal fusion.
An alternative to spinal fusion that has been given much attention is the use of intervertebral disc arthroplaty devices, such as articulating artificial disc devices. Several different types of intervertebral disc arthroplasty devices have been proposed for preventing the collapse of the intervertebral space between adjacent vertebrae while maintaining a certain degree of stability and range of pivotal and rotational motion therebetween. Such devices typically include two or more articular elements that are attached to respective upper and lower vertebrae. The articular elements can be anchored to the upper and lower vertebrae by a variety of methods, including the use of bone screws that pass through corresponding openings in each of the elements and thread into vertebral bone, and/or by the inclusion of spikes or teeth that penetrate the vertebral endplates to inhibit migration or expulsion of the device. The articular elements are typically configured to allow the elements, and correspondingly the adjacent vertebrae, to pivot and/or rotate relative to one another.
For a variety of reasons, it is sometimes necessary to take remedial measures as a result of a failure of an artificial disc devices or to immobilize a motion segment for other reasons. For example, it is possible that an artificial disc could become displaced from its intended position, possibly resulting in or resulting from damage or weakening of surrounding bone. Moreover, in the case of articulating discs, it is possible that the articulating interfaces could become inoperable due to wear or due to the presence of foreign objects that interfere with its operation. Remedial measures can include, for example, replacement of an artificial disc with a new disc arthroplaty device or fusion of the motion segment.
There is a continuing need for advancements in the relevant field, including new devices, systems and methods for remedying a failed artificial disc and devices, systems and methods for immobilizing a spinal motion segment for other reasons. The present application addresses this need and provides a variety of additional benefits and advantages.